Electromechanical device



July 3Q, 3946. w. R. HARRY ET AL ELECTROMECHANICAL DEVICE 2 Sheets-Sheet2 Filed Oct. 15, 1941 M/VENTORS:

(Rf/ARR) By FFROMANOW ATTOR/VE Patented July 30, 1946 ELECTROMECHANICALDEVICE William R. Harry, New York, N. Y., and Frank F. Romanow, BerkeleyHeights, N. J., assignors to Bell Telephone Laboratories, Incorporated,New York, N. Y., a corporation of New York Application October 15, 1941,Serial No. 415,032

2 Claims.

The invention relates to electromechanical devices and more particularlyto a signal pressure variation or wave detector or microphone for use ina liquid wave transmission medium, for eX- ample, water.

An object of the invention is to enable the detection with a singledevice of submarine signals or disturbances in both the audio andsuperaudio portions of the frequency range.

A further object is to improve the structure and performance ofsubmarine signal detectors or microphones.

A feature of the invention comprises a submarine signal detector ormicrophone of the pressure gradient type.

A further feature comprises a submarine signal detector or microphone inwhich the signal responsive element is a coil disposed in a magneticfield and adapted to move therein in response to the pressure gradientestablished between different portions of the coil by the signalpressure variations.

Still another feature comprises a submarine signal detector ormicrophone in which the signal responsive element is a coil exposed tothe liquid medium.

A submarine signal detector or microphone in accordance with thisinvention comprises a coil of many turns of fine wire, supported formovement in a magnetic field, and adapted to be exposed to the water inwhich the microphone is submerged or immersed. The coil may have a pairof elongated portions each of which is exposed to the water on oppositesides or surfaces of the microphone structure which may be a somewhatflat, elongated rectangular structure. Signal pressure variations orsignal waves in the water originating on either side of the microphoneare effective on each of the elongated coil portions, the coil movementbeing determined by the difierence in the phases of the signal pressurevariation or wave acting on the two portions. With each elongated coilportion positioned in a separate magnetic field and with the magnetelements producing the magnetic field properly poled, the currentsgenerated in the coil portions by movement thereof in the magneticfields will be cumulative.

A more complete understanding of this invention will be obtained fromthe detailed description that follows taken in conjunction with theshowings of the appended drawings wherein:

Fig. 1 is a top plan view of a microphone embodying this invention;

Figs. 2 and 3 are a front and a side elevational View, respectively, ofthe microphone of Fig. 1;

Fig. 4 is an enlarged cross-sectional view of the microphone of Fig. 1taken along the line 44 of Fig. 2;

Fig. 5 is an exploded perspective showing of the microphone of Figs. 1to 4 to evidence struc tural details more clearly;

Fig. 6 is a view, partly broken away and partly in section, of one endof the microphone of Figs. 1-5 to show more clearly the manner in whichthe coil is supported; and

Fig, '7 illustrates how the microphone may be suspended or immersed in aliquid medium.

With reference to the drawings, there is shown a microphone lllembodying the invention. It comprises a plurality of elongated magnetsH; [2, I3, I4 that may be of any suitable magnetic material, magnetizedso that their poles are at the larger and smaller bases of each asindicated in Fig. 4. The magnets are arranged in two oppositely disposedpairs with their narrower or tapered bases providing spaced planar polefaces l5, defining two air-gaps l6, ll. The pole faces are maintained ata preassigned separation by the projections 18 on metallic spacer orseparator members ill of non-magnetic material at the upper and lowerends of the microphone. The ends of each pair of magnets fit intogrooves or slots 20, 2| in the upper and lower surfaces of nonmagneticblocks or members 22, 23, respectively. The upper surface of each member23 contains a groove or slot 24 adapted to receive the horizontalportion of an L-shaped terminal 25 which is fastened to the block by asuitable member 2%.

The members I9, 22, 23 contain passages 21, 2B, 29 between their lateralvertical surfaces which are in alignment when the magnet ends are in theslots 20, 2| and the shoulder portions 30-0f the member [9 rest on theends of the magnet with projection [8 extending into the air-gap. Themagnet and the members i9, 22, 23 are clamped between two elongatedstrips or plates 3| of magnetic material by fastening members 32, 33,the stem of each member 32 extending through the apertures in the strips3! and the passages 21, 28, 29 and being engaged on its threaded end bymember 33. The substantially V-shaped space or chamber 56 formed by eachpair of magnets is closed by an elongated strip or insert '34 ofnon-magnetic material, whose outer surface is substantially in the sameplane as that of the pole faces. The upper and lower extremes of thesespaces are closed by the adjacent surfaces of the members 22, 23 and bythe shoulders 30 of the member l9. Hence, when the device is immersed inwater, the water does not enter these spaces, or, if it does, it canhave no eifect on movement of the coil 35 now to be described. Ifdesired, the magnets, the inserts 34, the spacers l9 and the strips 3imay be soldered together where adjacent, to constitute a unitarystructure.

The coil 35 comprises a spool or channel member of insulating or ofnon-magnetic material on which is wound many turns of fine insulatedwire 36. The spool comprises a pair of elongated planar rectangularportions 31 spacedapart by a frame portion 38 to form a peripheralchannel or recess in which the wire 36 is located. The spool materialmay be Bakelite; after the wire has been wound in the channel, it may bevacuum impregnated in a Bakelite varnish medium. Instead of Bakelite,the spool material may be aluminum. The ends 39 of the winding may bebrought out to the terminals 25. The coil is supported in the air-gapsl5, ll by U-shaped spring metal members or yokes 40 slipped over andfastened to each end of the coil and flexible spring members Al. Each ofthe latter is soldered at one end to an outwardly projecting tab orextension 42 of a. member 10, and at its other end 43 is soldered to aspacer member l9. Each member 4| has a longitudinal boss or ridge 45 tostiffen it, and is surrounded by a cover or sleeve 44 of dampingmaterial, such as rubber. The members M permit movement of thecoil intwo directions 180 degrees removed, that is, to and fro in the air-gapswith the planar portions 31 of the spool moving substantially parallelto the pole faces; constrain the coil against movement in otherdirections; and aid in minimizing undesirable or parasitic vibrations inthe coil.

The spaces or passages existing between the side walls Or surfaces ofthe spool and the magnet structure, that is, the spaces between thespool portions 31 and the pole faces and the insert 34 are such that avery high impedance is presented to signal pressure variations or wavesof frequencies within the band of frequencies to which the microphone isintended to be responsive. When the device is immersed in water, thewater may flow between the front and the back of the microphone throughthese spaces, that is, between the two large surfaces of the microphone,but signal pressure variations or waves must travel around themicrophone in order to be effective On each vertical or air-gap portionof the coil. The mass of the coil is proportioned so as to be equalapproximately to the radiation mass of water.

The microphone may be supported under water as shown in Fig. '7 by asuitable cable 50 which may include the conductors for connecting themicrophone at the terminals 25 with suitable electrical equipment at anobserver or recording station, for analysis or indication of theresponse of the microphone to signal or other under-water disturbancesof a frequency or frequencies within the range to which the microphoneis responsive.

In a microphone constructed in accordance with the invention, the actualdimensions were approximately one-half those of Figs. 1, 2 and 3. Themagnet members Il--l4 were of an aluminum-nickel-cobalt-steel alloy(AL-%; Ni- 17%; Cu-6%; Co-12%; Fe and C balance); the air-gaps wereapproximately .125 inch wide and approximately 2.5 inches long; theclamping strips 3| were of Swedish steel. The flux density at the polefaces was of the order of 1800 4 gauss. The spool for the coil was ofBakelite; the conductor for the spool was of No. 33 B. and S.enamel-coated aluminum wire, and comprised approximately 62 turns. Thecoil supports were of phosphor bronze, the thickness of the strip fromwhich they were formed being approximately .002 inch. A microphone inaccordance with this invention will respond under water to sonic orsupersonic signal waves or disturbances over a wide frequency range, forexample, up to 60,000 C. P. S. or greater.

The'microphone described hereinabove may be used as a standardmicrophone for calibrating microphones of similar or difierentconstruction intended for use in a liquid medium, and, specifically,under water for detecting marine or submarine signals or disturbances.Such signals or disturbances might be those created with a suitablesource under water for communications or sounding purposes, or mightcomprise the underwater sonic or supersonic Waves developed byparticular marine craft or equipment, such as, ships, submarines, shipengines, etc.

The microphone described is of the pressure gradient type, i. e., itswave-responsive element or coil is movable in response to the pressuregradient or difference in pressure established between differentportions thereof by the signal wave or disturbance. The coil is exposedat the front and back of the microphone, i. e, the largearea portionsthrough which the elongated winding portions are observable. The signalwave or disturbance has access, therefore, to each of the elongated coilportions. If the wave is incident on each elongated coil portion in thesame phase, the coil does not move, but if the incoming wave ordisturbance is incident out of phase on the coil portions, the coil willbe caused to move to an extent dependent on the intensity of the waveand the magnitude of the phase difference. The microphone has adirectional response characteristic, and may be arranged to bemaintained stationary, or adapted for adjustment in position dependenton the advantage desired to be taken of such characteristic.

Although this invention has been disclosed with reference to what isbelieved at this time to be a preferred embodiment, it is apparent thatit is not limited thereto, its scope being evidenced by the appendedclaims.

What is claimed is:

1. A device for detecting signal pressure variations in a liquid medium,said device comprising a coil, means to support said coil to expose thecoil directly to the liquid medium, means providing a magnetic fieldhaving an air-gap, said supporting means disposing saidcoil in saidair-gap for translational movement in said magnetic field in response topressure gradient set up between different portions of said coil by thesignal pressure variations, said air-gap allowing a mechanical clearancebetween the coil and magnetic polepieces sufiicient to allow the liquidmedium to flow therebetween but small enough to present high impedanceto the signal pressure variations.

2. A device according to claim 1 in which said coil is rectangular inshape with one dimension many times longer than the other and saidsupporting means comprises a fixed frame surrounding the coil and U-shaped spring'members slipped over the ends of the coil and havingtheir extremities resiliently supported. from the ends of said frame.

WILLIAM R. HARRY. FRANK F. ROMANOW.

